Self-Balancing Electric Unicycle By MIT Student

MIT student Stephan Boyer has created a self-balancing electric unicycle to get around campus.

(Self-Balancing Electric Unicycle video)

To estimate its orientation, Bullet integrates readings from the gyro and accelerometer using a complementary filter. To balance, the angle estimate is fed through a PID loop (with no integral term). The loop runs at 625 Hz. The output from this stage determines the duty cycle of a 1.22 kHz PWM signal, which is connected to the H-bridge. The code was written in C, and is in the public domain...

I expect that most undergraduates in electrical engineering could probably reconstruct the circuit given this description, burn the code onto the microcontroller, and have a working electric unicycle controller. A trip to the machine shop to construct the chassis and voilą, you've made your very own self-balancing unicycle!

He calls it the Bullet, but sf fans already have a name for this kind of device; the tumblebug, from Robert Heinlein's 1940 novella The Roads Must Roll:

Gaines and Harvey mounted tumblebugs, and kept abreast of the Cadet Captain, some twenty-five yards behind the leading wave. It had been a long time since the Chief Engineer had ridden one of these silly-looking little vehicles, and he felt awkward. A tumblebug does not give a man dignity, since it is about the size and shape of a kitchen stool, gyro-stabilized on a single wheel...